An inflator is utilized in a motor vehicle to rapidly fill an inflatable cushion during a crash. Inflatable cushions are commonly known in the art as airbags. Motor vehicles typically have multiple airbags that are filled with inflation gas from inflators to protect the vehicle occupants from injuries during a crash. The airbag functions by absorbing the vehicle occupant's kinetic energy in a controlled manner to reduce the deceleration forces experienced by the vehicle occupant.
The inflator is a gas-generating device that rapidly produces inflation gas, which is utilized to fill a folded airbag. The pyrotechnic inflator, a commonly utilized inflator in the safety restraint industry, generates inflation gas by burning a gas generant. The gas generant contains a blend of fuel and oxidizer, and upon ignition produces gaseous combustion products. The pyrotechnic inflator may have one or more chambers containing gas generant. A pyrotechnic inflator having gas generant in two chambers, which are ignited independently by two igniters is referred to herein as a dual stage inflator.
The dual stage inflator has several contemplated firing scenarios. First, the primary chamber is fired whereby a fixed quantity of inflation gas is produced. Second, the primary chamber is fired and after a predetermined delay, the secondary chamber is fired. Third, the primary chamber and the secondary chamber are fired simultaneously. The gas output profile, which is a plot of gas pressure in the airbag as a function of time, varies in all of the firing scenarios. The dual stage inflator has the flexibility to tailor the gas output to afford maximum protection to different vehicle occupant sizes and positions.
Many variants of the dual stage inflator have been developed. One variant includes a pancake shaped inflator having a divider plate extending across the length of the inflator dividing the inflator into two stages or combustion chambers. A co-assigned patent, U.S. Pat. No. 6,199,906, along with co-assigned patent application Ser. No. 10/640031, teach a pancake shaped inflator having a first and second gas combustion chambers arranged in a manner where one combustion chamber is stacked on top of the other combustion chamber. Because of the need for dual stage inflators in the safety restraint industry, there is a desire to design cheaper and more reliable dual stage inflators.